The present invention relates to a power source apparatus for extracting a plurality of voltage outputs from a single transformer.
In a conventional copying machine, a printer or the like of an electrophotographic system, a sequence control low voltage power source apparatus, an exposure power source apparatus, and a charging high voltage source apparatus are separately used. For example, the charging high voltage power source apparatus is arranged such that a stabilized low voltage output (normally, 24 V) is boosted to a voltage of 5 to 9 kV by a DC/DC inverter. FIG. 20 shows an arrangement of the charging high voltage power source apparatus.
The power source apparatus includes a converter transformer T. An AC voltage from a commercial power source 503 is rectified and smoothed by a rectifying/smoothing circuit 502 and the resultant DC voltage is applied to a primary winding 501 of the converter transformer T. The DC voltage is driven and turned on/off in response to a switching pulse generated by a PWM (Pulse Width Modulation) control circuit 504. A damper diode D61 and a resonance capacitor C60 are connected in parallel with a transistor Q60. The ON/OFF operation of the DC voltage derives an output in accordance with a winding ratio of secondary windings 521 and 522 of the transformer T.
In the power source apparatus, low voltage outputs appear at the secondary windings 521 and 522 and are rectified by rectifying diodes D62 and D63 and smoothed by smoothing capacitors C61 and C62, thereby obtaining a low voltage DC output. A high voltage DC output is obtained by boosting the low voltage DC output by DC/DC converters 505 and 506. This arrangement aims at obtaining a stable high voltage output regardless of variations in the low voltage output.
In the above arrangement, transformers are used in both DC/DC converters 505 and 506. The numbers of transformers and driving circuits used in the power source apparatus are large, and resulting in a bulky power source apparatus at high cost. In addition, power efficiency is also degraded. These disadvantages are common in power source apparatuses used in various types of equipment in addition to the power sources for electrophotographic apparatuses.
As described in U.S. patent application Ser. No. 904,810, a method of integrating the transformers is proposed. However, as soon as the power switch is turned on, a high voltage output is generated, and high voltage control is difficult. In addition, a safety problem is also presented.